Q: What about installing the heat pump in a greenhouse? Maybe removable for the summer.
A: I have not done this in a greenhouse but I think it is a good idea. Effectively I have done this by bringing plants indoors in the fall and keeping them in our sunroom. The sunroom receives a very small amount of heat from our house heat pumps (it is at the end of the ductwork) but, using LED grow lights (powered by my solar panels) I was able to get red ripe peppers at Christmas. They tasted great!